1. Field of the Invention
The present invention generally relates to a signal recording and/or reproducing apparatus and, more particularly, to a characteristics corrector in the signal recording and/or reproducing device for automatically correcting a distortion resulting from the non-linearity in a signal processing system during the recording or reproduction and for automatically correcting the level of a reproduced signal.
2. Description of the Prior Art
In a signal recording and/or reproducing apparatus such as, for example, a magnetic video tape recording and/or reproducing apparatus (hereinafter referred to as a video tape player), one of the methods of recording a wide band video signal which is well known includes a channel division recording system. According to the channel division recording system, a single signal is divided into a plurality of channels so that the band width required for each channel can be reduced prior to the actual recording of the signal.
In the channel division recording method, if the signal to be recorded is a television signal, the signal is divided into a plurality of channels one for each horizontal scanning period. Finally the time-axis of the signal of each channel is expanded.
The channel division recording method is illustrated in FIG. 1 of the accompanying drawings. In the illustrated example, the input video signal is shown as divided into two channels CH.A and CH.B. The waveform (a) shown in FIG. 1 is the one of an input signal wherein characters H1, H2, H3, H4, . . . represent successive horizontal scanning periods, respectively. The input signal is divided into the channels CH.A and CH.B alternately for each horizontal scanning period with the time-axis thereof expanded to represent such waveforms as shown by (b) in FIG. 1.
When, by this division, the time-axis of the signal is expanded, the band width of each channel is reduced. However, since the signal can be recorded or reproduced in two systems, deterioration of picture qualities such as the appearance of scanning lines tends to occur when there is a difference in characteristics between these channels. In view of this, a device for automatically compensating for the difference in characteristics between the channels is necessitated.
One example of the characteristics corrector hitherto used in the video tape player, wherein the recording or reproduction is carried out by the division of the video signal into a plurality of channels as hereinabove described, is disclosed by Seishi Sasaki et al. in their papers "WIDE BAND VIDEO SIGNAL RECORDER HAVING LEVEL AND LINEARITY CORRECTOR" (IEEE Transactions on Consumer Electronics, vol. CE-32, No. 3, Aug. 1986) and "VTR for Bandwidth-compressed Hi-vision" (National Technical Report Vol. 32, No. 4, Aug. 1986). The characteristics corrector disclosed in the previously mentioned paper is reproduced in FIG. 2 of the accompanying drawings in schematic block circuit representation. Referring to FIG. 2, reference numeral 13 represents a memory for the storage of a reproduced ramp signal; reference numeral 14 represents an adding, averaging and checking circuit operable to perform an adding, averaging and checking of the reproduced ramp signal; reference numeral 15 represents a level correction table memory for the storage of a level correction table; reference numeral 16 represents a data memory for the storage of data of a reference ramp signal data; reference numeral 17 represents a data processing circuit; reference numeral 18 represents a switch for switching over addresses of the level correction table memory 15; reference numeral 19 represents an input terminal to which the reproduced signal is applied; reference numeral 20 represents an input terminal to which the reproduced ramp signal is applied; reference numeral 21 represents a time-axis data terminal; and reference numeral 22 represents a corrected output terminal.
While the prior art characteristics corrector is so constructed as hereinabove described, the ramp signal varying from a black level to a white level is recorded during a vertical blanking period of the video signal. Further, by reproducing such ramp a signal, the reproduced level can be coordinated with the recorded level. Assuming that the ramp signal, which had represented such a waveform as shown by (a) in FIG. 3 when recorded, represents such a distorted waveform as shown by (b) in FIG. 3 when reproduced, the reproduced ramp signal is supplied to a time base corrector (TBC) to adjust the time-axis thereof. This is so that the ramp signal during the recording can be matched in timing with that during the reproduction. This thereby renders the reproduced output level so as to match with the level of the input signal.
To describe the operation in detail, in FIG. 2 the reproduced ramp signal is first inputted to the adding, averaging and checking circuit 14 at which point a plurality of ramp signals are added together. This is to improve the signal-to-noise ratio. They are then checked as to the waveform of the reproduced ramp signal which has been averaged. This thereby eliminates any effect such as a dropout. The reproduced ramp signal which has been added, averaged and checked is subsequently stored in the reproduced ramp data memory 13 with the time-axis data used as an address. Then, the data stored in the reproduced ramp data memory 13 and the address are reversed and stored in the level correction table memory 15. The reference ramp signal data memory 16 stores therein the waveform of the ramp signal therein, which had been exhibited at the time of recording. Therefore, when a reproduced video signal data is applied through the switch 18 as an address of the level correction table memory 15, the address of the reference ramp signal data memory 16 is determined. Thus, the video signal data wherein the level correction is affected to an output of the reference ramp signal data memory 16, can be obtained.
The prior art characteristics corrector of the above described construction has the following problems. Since the timing of the ramp signal during the recording and that during the reproduction are required to be completely matched with each other, a highly precise time base corrector is necessitated. However, in the event of the occurrence of variation of the time-axis during one horizontal scanning period which is generally referred to as a velocity error, the timing of the ramp signal during the recording and that during the reproduction cannot be completely matched with each other during the latter half of the horizontal scanning period. Therefore, the recording level and the reproducing level cannot be coordinated with each other.
Also, with the signal such as the ramp signal used in the prior art device, wherein the period during which the level of the video signal represented by the ramp signal is of the same level and is short, displacement of the sampling position results in the receipt of an erroneous reproduced ramp data. Therefore, an accurate level correcting operation cannot be accomplished.